This invention relates to an icebreaking method for opening a passage through an ice field and to an icebreaker for carrying out the method.
An icebreaker is designed to assist vessels in winter traffic. Such assistance includes opening or maintaining passages through ice fields. Therefore an icebreaker usually is designed to be suitable for a particular winter traffic pattern. For example for the Gulf of Finland it is typical that the number of vessels requiring assistance is large and the distance over which assistance is required is relatively small. The size of the vessels to be assisted varies greatly which sets special requirements on the width of the channel the icebreaker makes. The width of a vessel to be assisted in the Gulf of Finland is typically in the range from 10 to 40 m.
A conventional icebreaker cannot effectively assist a vessel the width of which exceeds the width of the icebreaker. On the other hand it is relatively seldom that very wide vessels need to be assisted so it would not be economic to build for example a 40 m wide icebreaker only for the few occasions on which such a wide icebreaker is needed. Hitherto it has been conventional to assist a wide vessel either by using one icebreaker to open a wide passage by going back and forth or by using two icebreakers at the same time together to open a wide passage. The first mentioned method is slow and rather ineffective, especially if the ice field is moving. The second method requires two icebreakers, which impairs the ability of the icebreaker fleet to render assistance elsewhere.
According to U.S. Pat. No. 5,218,917, the direction of movement of an icebreaker in heavy ice conditions may be different from its direction of movement in open sea and light ice.